//原始代码
setTimeout(function (){
    var a = 'hello'
    setTimeout(function (){
        var b = 'lagou'
        setTimeout(function (){
            var c = 'I ♥ U'
            console.log(a + b + c)
        },10)
    },10) 
},10)           

//promise方法
const promise  = new Promise(function(resolve, reject){
    resolve('hello');
})

promise.then(value => {
    return 'hello'
}).then(value => {
   // console.log(value)
    return value + 'lagou'
}).then(value => {
   console.log(value + 'I ♥ U')
    return value + 'I ♥ U'
}).then(value => {
    return value 
})

 